US20230025678A1 - Non-oriented electrical steel sheet and method for manufacturing same - Google Patents

Non-oriented electrical steel sheet and method for manufacturing same Download PDF

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US20230025678A1
US20230025678A1 US17/786,508 US202017786508A US2023025678A1 US 20230025678 A1 US20230025678 A1 US 20230025678A1 US 202017786508 A US202017786508 A US 202017786508A US 2023025678 A1 US2023025678 A1 US 2023025678A1
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steel sheet
electrical steel
oriented electrical
annealing
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Hyung Don JOO
Il-Nam YANG
Junesoo Park
Chang Soo Park
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Posco Holdings Inc
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Posco Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
    • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
    • H01F1/147—Alloys characterised by their composition
    • H01F1/14766—Fe-Si based alloys
    • H01F1/14775—Fe-Si based alloys in the form of sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
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    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/78—Combined heat-treatments not provided for above
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    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
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    • C21D6/00—Heat treatment of ferrous alloys
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
    • C21D8/1222—Hot rolling
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
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    • C21D8/1233—Cold rolling
    • C—CHEMISTRY; METALLURGY
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D8/1255—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest with diffusion of elements, e.g. decarburising, nitriding
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D8/1261—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest following hot rolling
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
    • C21D8/1272—Final recrystallisation annealing
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1277—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties involving a particular surface treatment
    • C21D8/1283—Application of a separating or insulating coating
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
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    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
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    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C—CHEMISTRY; METALLURGY
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding
    • C23C8/26—Nitriding of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
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    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/80—After-treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
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    • C—CHEMISTRY; METALLURGY
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    • Y02T10/64—Electric machine technologies in electromobility

Definitions

  • An embodiment of the present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, an embodiment of the present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof that may improve magnetism by appropriately adding Si and Sn, and improving texture through nitriding.
  • a non-oriented electrical steel sheet is used as a material for an iron core in rotary devices such as motors and generators, and stationary devices such as small transformers, and plays an important role in determining energy efficiency in electric devices.
  • the representing characteristics of the electrical steel sheet may include iron loss and magnetic flux density, wherein it is preferable that the iron loss becomes smaller and the magnetic flux density becomes higher, and this is because when a magnetic field is induced as the iron loss becomes small the energy being lost in the form of heat can be reduced, and as the magnetic flux density becomes high a larger magnetic field can be induced with the same amount of energy.
  • h, k, I, u, v, and w are integers.
  • all grain sizes are larger than the thickness, and have a structure penetrating the thickness. Since the non-oriented electrical steel sheet is manufactured as complex shapes such as motor cores through punching processing, when the grain size is excessively large, the workability is very poor.
  • a method for forming a ⁇ 100 ⁇ plane parallel to a surface of a metal plate has been presented on the surface of the metal plate.
  • the method for forming the ⁇ 100 ⁇ surface of the surface of the metal plate includes: reducing oxygen in at least one of an inner region and a surface region of the metal plate or heat-treating the metal plate under a temperature at which an austenite phase is stable while blocking the metal plate from external oxygen; and phase-transforming the heat-treated metal plate into a ferrite phase.
  • This method requires a vacuum heat treatment that is difficult to implement industrially because it is necessary to block oxygen from the outside, and it requires a lot of heat treatment time, so it is a very difficult process for industrial success.
  • iron loss in the case of iron loss, it may be expressed as a sum of hysteresis loss, eddy current loss, and abnormal eddy current loss, while in the case of high-frequency characteristics, a ratio of eddy current loss increases, so a method other than texture control, which is important for hysteresis loss, is required.
  • Factors that significantly affect the eddy current loss include resistivity, a sheet thickness, and a grain size. The resistivity and thickness of the steel sheet are as described above.
  • the eddy current loss decreases when the grain size decreases.
  • the hysteresis loss increases, and accordingly, an optimum grain size is set.
  • the optimum grain size of a steel sheet for a high frequency motor is smaller than the optimum grain size of a general low frequency therefor.
  • the eddy current is mainly formed on the surface due to the skin depth effect, so that it is necessary to refine the surface grains or increase the surface resistivity.
  • the skin depth When a high-frequency current flows, the current is concentrated on a surface of a conductor, and a depth at which 1 ⁇ e (36.5 %) of the surface current flows is called the skin depth.
  • ⁇ (2 ⁇ / ⁇ ) ⁇ 0.5 -503.3*( ⁇ / ⁇ rf) ⁇ 0.5
  • ⁇ skin depth [m]
  • ⁇ electrical resistivity [ ⁇ m]
  • ⁇ r relative permeability
  • f frequency
  • the approximate skin depth is 200 ⁇ m at 50 Hz, while it becomes thinner at 100 ⁇ m at 400 Hz and 35 ⁇ m at 2000 Hz. Accordingly, when the grains in the surface layer are made to be small, the eddy current loss is reduced, so that the formation of the eddy current formed on the surface at the high frequency is prevented, and thus the high frequency iron loss may be improved. In addition, it is possible to reduce the iron loss by reducing the hysteresis loss by increasing the central grain size, and particularly, it is possible to improve the low frequency iron loss, or at least to prevent deterioration.
  • a method of forming a nitride and/or internal oxide-containing layer of which an average particle diameter of nitrides and/or internal oxides deep from the surface layer of the steel sheet in the surface layer of the steel sheet and an area ratio in a cross-section of the sheet thickness are regulated within a predetermined range, and of regulating an area ratio of nitrides and internal oxides present in regions other than at the nitride and/or internal oxide-containing layer within the sheet thickness cross-section and an average grain diameter D of the steel sheet within a predetermined range, has been known.
  • the production state of the nitrides and internal oxides and their average particle diameters were controlled by adjusting the annealing temperature, annealing time, and annealing atmosphere (N 2 concentration, dew point, and the like).
  • the particle diameters of the internal oxides and nitrides were mainly controlled by changing the annealing temperature and annealing time
  • the formation depths of the internal oxide-containing layer and the nitride-containing layer were mainly controlled by changing the annealing time and annealing atmosphere
  • the area ratios of the internal oxides and nitrides in the cross-section of the sheet thickness were mainly controlled by changing the annealing atmosphere and the annealing temperature.
  • the coarse oxides and nitrides when used, they must be contained in a very large amount to control the grain size, and it is difficult to efficiently control them in a short time.
  • An embodiment of the present invention provides a non-oriented electrical steel sheet and a manufacturing method therefor. Specifically, an embodiment of the present invention provide a non-oriented electrical steel sheet and a manufacturing method thereof that may improve magnetism by appropriately adding Si and Sn, and improving texture through nitriding.
  • a non-oriented electrical steel sheet according to an embodiment of the present invention includes, in wt%, Si: 2.2 to 4.5 %, Mn: 0.5% or less (excluding 0 %), AI: 0.001 to 0.5 %, Sn: 0.07 to 0.25 %, and N: 0.0010 to 0.0090 %, and the balance of Fe and inevitable impurities.
  • a surface layer portion existing in an inner direction from a surface of the steel sheet and a central portion existing inside the surface layer portion are included, and the central portion includes N at 0.005 wt% or less, and the surface layer portion further includes N at 0.001 wt% or more compared to the central portion; and the surface layer portion has an average grain size of 60 ⁇ m or less, and the central portion has an average grain size of 70 to 300 ⁇ m. Specifically, an average grain size of the central portion may be 70 to 130 ⁇ m.
  • the non-oriented electrical steel sheet according to the embodiment of the present invention may further include one or more of C: 0.005 wt% or less and S: 0.003 wt% or less.
  • the non-oriented electrical steel sheet according to the embodiment of the present invention may further include one or more of Sb: 0.2 wt% or less and P: 0.1 wt% or less.
  • the non-oriented electrical steel sheet according to the embodiment of the present invention may further include one or more of Cu: 0.015 wt % or less, Ni: 0.05 wt % or less, Cr: 0.05 wt % or less, Zr: 0.01 wt % or less, Mo: 0.01 wt% or less, and V: 0.01 wt% or less.
  • the surface layer portion may include a nitride, and an average particle diameter of the nitride may be 10 to 100 nm.
  • An average grain size of the central portion may be twice or more an average grain size of the surface layer portion.
  • a fraction of grains having an angle between a ⁇ 100 ⁇ plane and a rolling surface of 15° or less may be 30 % or more.
  • a fraction of grains having an orientation deviated of 15° or less from a ⁇ 001 ⁇ 012> orientation may be 20 % or more.
  • An intensity of a ⁇ 001 ⁇ 012> orientation of the central portion may be 7 times or more random thereof when expressed as an orientation distribution function (ODF).
  • ODF orientation distribution function
  • a fraction of grains having an angle between a ⁇ 111 ⁇ plane and a rolling surface of 15° or less may be 25 % or less.
  • the non-oriented electrical steel sheet may satisfy B 50 /B s ⁇ 0.84.
  • B 50 represents a magnitude (Tesla) of magnetic flux density induced when a magnetic field of 5000 A/m is added
  • Bs represents a saturation magnetic flux density value (Tesla)
  • W 15/50 may be 1.94 W/kg or less
  • W 10/1000 may be 43 W/kg or less.
  • W 15/50 represents an average loss in a rolling direction and a direction perpendicular to the rolling direction when a magnetic flux density of 1.5 Tesla is induced at a frequency of 50 Hz
  • W 10/1000 represents an average loss in the rolling direction and the direction perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 1000 Hz).
  • a manufacturing method of a non-oriented electrical steel sheet includes: hot-rolling a slab that includes, in wt%, Si: 2.2 to 4.5 %, Mn: 0.5 % or less (excluding 0 %), AI: 0.001 to 0.5 %, Sn: 0.07 to 0.25 %, and N: 0.005 % or less (excluding 0 %), and the balance of Fe and inevitable impurities, to manufacture a hot-rolled sheet; cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and final annealing the cold-rolled sheet.
  • the final annealing includes: a step of nitriding-annealing and a step of annealing grain growth; when a temperature is increased for the nitriding-annealing of the cold-rolled sheet, a temperature increase rate from 300° C. to a nitriding-annealing temperature is 30° C./s or more; in the nitriding-annealing, an amount of nitriding is 10 to 80 ppm by weight; and a temperature of the annealing of the grain growth is 960 to1200° C.
  • a final reduction ratio may be 60 to 88 % in the manufacturing of the cold-rolled sheet.
  • a temperature of the nitriding-annealing may be 700 to850° C.
  • the nitriding-annealing may be performed in an atmosphere containing ammonia, nitrogen, and hydrogen.
  • the embodiment of the present invention by differently controlling precipitates in a thickness direction by contents and nitriding of Si, Mn, Al, and Sn among alloy elements added to steel to control a grain size, it is possible to manufacture a non-oriented electrical steel sheet with excellent high-frequency iron loss and also excellent low-frequency iron loss.
  • FIG. 1 illustrates a schematic view of a cross-section of a non-oriented electrical steel sheet according to an embodiment of the present invention.
  • first, second, third, etc. may be used herein to describe various elements, components, regions, areas, zones, layers, and/or sections, they are not limited thereto. These terms are only used to distinguish one element, component, region, area, zone, layer, or section from another element, component, region, layer, or section. Therefore, a first part, component, region, area, zone, layer, or section to be described below may be referred to as second part, component, area, layer, or section within the range of the present invention.
  • % means wt%, and 1 ppm is 0.0001 wt%.
  • inclusion of an additional element means replacing the balance of iron (Fe) by an additional amount of the additional elements.
  • a non-oriented electrical steel sheet according to an embodiment of the present invention includes, in wt%, Si: 2.2 to 4.5 %, Mn: 0.5 % or less (excluding 0 %), AI: 0.001 to 0.5 %, Sn: 0.07 to 0.25 %, and N: 0.0010 to 0.0090 %, and the balance of Fe and inevitable impurities.
  • Si is an element that increases specific resistance to lower eddy current loss of iron loss. When too little Si is added, it may be difficult to obtain low iron loss characteristics. On the other hand, when too much Si is added, plate breakage may occur. Accordingly, Si may be included in an amount of 2.5 to 4.0 wt%. Specifically, it may be included in an amount of 2.70 to 4.80 wt%. More specifically, it may be included in an amount of 2.90 to 3.50 wt%.
  • Mn manganese
  • saturation magnetic flux density decreases
  • Mn is an austenite forming element, so it is preferable to not be added in order to satisfy a range in which solid phase transformation does not occur.
  • an amount of Mn that does not form austenite may increase even if manganese is increased.
  • an amount of Mn may be 0.5 % or less in a range that does not form austenite, excluding 0 %.
  • Mn may be included in an amount of 0.01 to 0.50 wt%.
  • Aluminum (Al) is an element that lowers eddy current loss by increasing specific resistance, but the texture is changed as the content of AI increases. When too little AI is added, it reacts with a trace amount of N to form very fine AIN, which may deteriorate the magnetism. Conversely, when too much AI is added, an AI oxide is distributed on the surface, an AI nitride has a bad effect on magnetism, and it may make the coating adhesion inferior later. Accordingly, AI may be included in an amount of 0.001 to 0.500 wt%. Specifically, it may be included in an amount of 0.010 to 0.400 wt%.
  • Tin (Sn) as a grain boundary segregation element suppresses diffusion of nitrogen through the grain boundary, inhibits formation of ⁇ 111 ⁇ and ⁇ 112 ⁇ textures undesirable to magnetism, and increases ⁇ 100 ⁇ and ⁇ 110 ⁇ textures favorable to magnetism, so that it is an element added to improve magnetic properties.
  • Sn may be included in an amount of 0.070 to 0.250 wt%. Specifically, it may be included in an amount of 0.100 to 0.230 wt%.
  • the nitridation is first performed at a temperature before the segregation of Sn, and then grain growth annealing may be performed.
  • N Nitrogen (N) forms fine and long AIN precipitates to inhibit the growth of crystal grains, so it is preferable to not be added to a slab, but it may be included in an amount of 0.005 wt% or less in the slab in consideration of an amount unavoidably added in a steelmaking process. Specifically, it may be included in an amount of 0.003 wt% or less in the slab. Specifically, it may be included in an amount of 0.002 wt% or less. As will be described later with respect to the manufacturing process, in the embodiment of the present invention, the content of N is increased through the nitriding process.
  • the non-oriented electrical steel sheet to be finally manufactured may contain 0.0010 to 0.0090 wt% of N.
  • the contents of N in the surface layer portion and the central portion may be different from each other, and the aforementioned content of N means an average value in the entire steel sheet.
  • the non-oriented electrical steel sheet according to the embodiment of the present invention may further include one or more of C: 0.005 wt% or less and S: 0.003 wt% or leas.
  • Carbon (C) is combined with Ti, Nb, and the like to form carbide to degrade magnetism, and when used after processing from the final product to an electrical product, since iron loss increases due to magnetic aging to decrease efficiency of electrical equipment, it may be included in an amount of 0.005 wt% or less. Specifically, it may be included in an amount of 0.003 wt% or less.
  • S Sulfur
  • MnS and CuS which are fine precipitates, and deteriorates magnetic characteristics by inhibiting grain growth. Accordingly, an upper limit thereof may be limited to 0.003 wt%. Specifically, it may be included in an amount of 0.002 wt% or less.
  • the non-oriented electrical steel sheet according to the embodiment of the present invention may further include one or more of Sb: 0.2 wt% or less and P: 0.1 wt% or less.
  • Sb and P have an effect of improving the texture together with the Sn described above, and may be additionally added in the range described above.
  • the non-oriented electrical steel sheet according to the embodiment of the present invention may further include one or more of Cu: 0.015 wt % or less, Ni: 0.05 wt % or less, Cr: 0.05 wt % or less, Zr: 0.01 wt % or less, Mo: 0.01 wt% or less, and V: 0.01 wt% or less.
  • Cu, Ni, and Cr react with impurity elements to form fine sulfides, carbides, and nitrides, which have an undesirable effect on magnetism, so that contents thereof are limited to Cu: 0.015 wt% or less, Ni: 0.05 wt% or less, and Cr: 0.05 wt% or less.
  • Zr, Mo, and V are strong carbonitride forming elements, it is preferable to not be added as much as possible, but Zr: 0.01 wt% or less, Mo: 0.01 wt% or less, and V: 0.01 wt% or less may be included.
  • the balance includes Fe and inevitable impurities.
  • the inevitable impurities are impurities mixed in the steel-making and the manufacturing process of the grain-oriented electrical steel sheet, which are widely known in the field, and thus a detailed description thereof will be omitted.
  • the addition of elements other than the above-described alloy components is not excluded, and various elements may be included within a range that does not hinder the technical concept of the present invention. When the additional elements are further included, they replace the balance of Fe.
  • FIG. 1 shows a schematic view of a cross-section of a non-oriented electrical steel sheet according to an embodiment of the present invention.
  • a non-oriented electrical steel sheet 100 includes a surface layer portion 20 present in an inner direction from a surface of the steel sheet and a central portion 10 present in the surface layer portion 20 .
  • contents of nitrogen in the central portion 10 and the surface layer portion 20 are different by nitriding, and the nitride is concentrated in the surface layer portion 20 , thereby preventing deterioration of low-frequency iron loss.
  • a grain size of the surface layer portion 20 is refined by the nitride of the surface layer portion 20 , so that high-frequency iron loss may be improved.
  • the texture is improved, so that the magnetic flux density may also be improved.
  • the contents of nitrogen in the central portion 10 and the surface layer portion 20 are different.
  • the central portion 10 may include 0.005 wt% or less of N. This is the same as the content of N in the slab, meaning that nitrogen does not substantially penetrate to the central portion 10 in the nitriding process.
  • the surface layer portion 20 largely includes nitrogen of 0.0010 wt% or more compared to the nitrogen content of the central portion 10 . As described above, by varying the nitrogen content, the nitride may be concentrated in the surface layer portion 20 . A gradient of nitrogen content may exist in a thickness direction in the surface layer portion 20 and the central portion 10 , and the above-described nitrogen range means an average in the entire thickness.
  • 0.0010 to 0.0090 wt% of nitrogen may be included in the entire electrical steel sheet 100 .
  • the nitride may be precipitated on the surface layer portion 20 .
  • an average particle diameter of the nitride may be 10 to 100 nm.
  • the nitride may be an (Al, Si)N, (Al, Si, Mn)N, or AIN.
  • a grain size of the surface layer portion 20 is refined by the nitride of the surface layer portion 20 , while a grain size of the central portion10 are not refined, so their average grain sizes may be different from each other.
  • the surface layer portion 20 has an average grain size of 60 ⁇ m or less, and the central portion 10 has an average grain of 70 to 300 ⁇ m.
  • the low-frequency iron loss and high-frequency iron loss may be improved.
  • the central grain is controlled to be less than 300 ⁇ m.
  • an average grain size of the central portion may be 70 to 130 ⁇ m.
  • an average grain size of the surface layer portion 20 may be 20 to 55 ⁇ m, and the average grain size of the central portion 10 may be 70 to 120 ⁇ m.
  • the grain size refers to a diameter of an imaginary circle having the same area as the grain size. Measurement can be performed based on a surface parallel to a rolling surface (ND surface).
  • the average grain size of the central portion 10 may be twice or more the average grain size of the surface layer portion 20 .
  • the central portion 10 has improved texture, so that the magnetic flux density may also be improved.
  • a fraction of grains having an angle between the ⁇ 100 ⁇ plane and the rolling surface of 15° or less may be 30 % or more.
  • this value may be increased to 30 % or more by performing nitriding treatment together with Sn addition. Accordingly, a significant improvement in the magnetic flux density may be achieved.
  • the fraction of grains having the angle between the ⁇ 100 ⁇ plane and the rolling surface of 15° or less may be 30 % to 50 %.
  • a fraction of grains having an orientation deviated by 15° or less from a ⁇ 001 ⁇ 012> orientation may be 20 % or more.
  • the intensity of the ⁇ 001 ⁇ 012> orientation of the central portion 10 may be 7 times or more random when expressed as an orientation distribution function (ODF).
  • ODF orientation distribution function
  • a circumferential characteristic may be very good. Specifically, among the grains of the central portion 10 , a fraction of grains having an orientation deviated by 15° or less from a ⁇ 001 ⁇ 012> orientation may be 20 % to 40 %.
  • a fraction of grains having an angle between the ⁇ 111 ⁇ plane and the rolling surface of 15° or less may be 25 % or less.
  • the best orientation for magnetism is the ⁇ 100> orientation, followed by ⁇ 110>, and finally ⁇ 111> is the worst orientation.
  • the non-oriented electrical steel sheet has an ideal magnetic value when ⁇ 100> is uniformly arranged in the surface direction of the steel sheet, and in this case, when the ⁇ 112> orientation in the surface direction is strongly developed, the magnetism significantly deteriorates.
  • a volume fraction of grains in which the angle between the ⁇ 112 ⁇ plane and the rolling plane is 15° or less in the non-oriented electrical steel sheet including a high Si content without phase transformation it exists more than in the ⁇ 111 ⁇ orientation. This orientation also causes a lot of orientations bad for magnetism in the rolling surface direction, so it is necessary to lower the fraction of these orientations.
  • the fraction of grains having the angle between the ⁇ 111 ⁇ plane and the rolling surface of 15° or less may be 10 % to 25 %.
  • the magnetism may be improved.
  • the magnetic flux density is divided by this saturation magnetic flux density value according to the Si content, a degree of formation of the texture favorable to the magnetism through process improvement may be evaluated. That is, even if the high magnetic flux density may be obtained in a state of a low silicon content, since the iron loss has a very poor characteristic, the degree of the formation of the texture having the excellent magnetism with the low iron loss and the high magnetic flux density should be evaluated as a B 50 /B s value.
  • the non-oriented electrical steel sheet according to the embodiment of the present invention may satisfy B 50 /B s ⁇ 0.84.
  • B 50 represents a magnitude (Tesla) of magnetic flux density induced when a magnetic field of 5000 A/m is added, and Bs represents a saturation magnetic flux density value (Tesla)).
  • [Si], [Mn], and [Al] represent contents (wt%) of Si, Mn, and AI in the steel sheet, respectively.
  • W 15/50 may be 1.94 W/kg or less
  • W 10/1000 may be 43 W/kg or less.
  • W 15/50 represents an average loss in the rolling direction and the direction perpendicular to the rolling direction when a magnetic flux density of 1.5 Tesla is induced at a frequency of 50 Hz
  • W 10/1000 represents an average loss in the rolling direction and the direction perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 1000 Hz
  • a manufacturing method of a non-oriented electrical steel sheet includes: hot-rolling a slab that includes, in wt%, Si: 2.2 to 4.5 %, Mn: 0.5 % or less (excluding 0 %), AI: 0.001 to 0.5 %, Sn: 0.07 to 0.25 %, and N: 0.005 % or less (excluding 0 %), and the balance of Fe and inevitable impurities to manufacture a hot-rolled sheet; cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and final annealing the cold-rolled sheet.
  • the slab is hot-rolled.
  • the alloy components of the slab have been described in the alloy components of the above-described non-oriented electrical steel sheet, so duplicate descriptions thereof will be omitted. Since the alloy compositions are not substantially changed during the manufacturing process of the non-oriented electrical steel sheet, the alloy compositions of the non-oriented electrical steel sheet and the slab are substantially the same.
  • the slab may include, wt%, Si: 2.2 to 4.5 %, Mn: 0.5 % or less (excluding 0 %), AI: 0.001 to 0.5 %, Sn: 0.07 to 0.25 %, and N: 0.005 % or less (excluding 0 %), and the balance of Fe and inevitable impurities.
  • the slab may have a component that does not form an austenite phase in a temperature range before a solid state.
  • the slab may be heated before hot-rolling.
  • the heating temperature of the slab is not limited, but the slab may be heated at 1050 to1200° C.
  • the slab heating temperature is too high, precipitates such as nitride, carbide, and sulfide present in the slab are re-dissolved and then finely precipitated during hot-rolling and annealing, thereby inhibiting grain growth and reducing magnetism.
  • a thickness of the hot-rolled sheet may be 2.0 to 2.3 mm.
  • a finish rolling temperature may be 800° C. or higher. Specifically, it may be 800 to1000° C.
  • the hot-rolled sheet may be wound at temperatures of 700° C. or less.
  • hot-rolled-sheet-annealing the hot-rolled sheet may be further included.
  • a temperature of the hot-rolled-sheet-annealing may be 900 to1150° C.
  • Sn may be excessively contained in the steel and grain growth may decrease.
  • the temperature of the annealing is too high, surface defects may occur.
  • the hot-rolled sheet annealing is performed in order to increase the orientation favorable to magnetism as required, and it may be omitted.
  • the annealed hot-rolled sheet may be pickled.
  • the hot-rolled sheet is cold-rolled to manufacture a cold-rolled sheet.
  • the cold-rolling is finally performed to a thickness of 0.10 mm to 0.35 mm.
  • the cold-rolling may be performed once, or two or more times with intermediate annealing therebetween.
  • a temperature of the intermediate annealing may be 850 to1150° C.
  • a final reduction ratio may be adjusted to 60 % to 88 %.
  • the cold-rolling reduction ratio is too low, the Goss orientation develops, and when it is too high, development of the ⁇ 111 ⁇ 112> orientation becomes stronger, so it may be adjusted within the above-mentioned range.
  • the reduction ratio of the one cold-rolling step is the final reduction ratio, and when the cold-rolling is performed twice or more, the reduction ratio in the last cold-rolling is the final reduction ratio.
  • the cold-rolled sheet is finally annealed. As described above, it is possible to improve magnetism by introducing a nitriding process in the embodiment of the present invention.
  • the final annealing step includes a step of nitriding-annealing and a step of annealing grain growth.
  • the temperature increase rate from 300° C. to the nitriding-annealing temperature may be 30° C./s or more.
  • an appropriate content of Sn, an appropriate cold reduction ratio, and a temperature increase rate are very important. This is because, when the temperature increase rate is increased, the growth of the ⁇ 111 ⁇ or ⁇ 112 ⁇ orientation is suppressed, so it is advantageous for the growth of the ⁇ 100 ⁇ orientation.
  • the temperature of the nitriding-annealing step may be 700 to 850° C.
  • nitriding treatment temperature is too high, nitriding may be difficult due to Sn segregation or formation of an oxide layer.
  • a diffusion amount may be too small. Specifically, it may be 750 to 800° C.
  • the nitriding-annealing step may be performed in an atmosphere including ammonia, nitrogen, and hydrogen.
  • the amount of nitriding may be increased from 10 to 80 ppm by weight through the nitriding-annealing.
  • the nitriding temperature is low, the nitrides are mostly present in the surface layer portion, but when the amount of nitriding is too large, the low-frequency iron loss may deteriorate.
  • the amount of nitriding is too small, there may be no effect of refining the grain in the surface layer portion.
  • the amount of nitriding may be 15 to 50 ppm by weight. The amount of nitriding is calculated based on the thickness of the entire electrical steel sheet 100 including the surface layer portion 20 and the center portion 10 .
  • the annealing of the grain growth may be performed at 960 to 1200° C. Since the content of Sn is high and the grain growth is suppressed, the final annealing may be performed within the above-described range.
  • the annealing time of the grain growth may be 65 seconds to 900 seconds.
  • the annealing time is too short, since the Sn content is high, the grain growth may be hindered by grain boundary segregation, and the size of the grains may be reduced.
  • the annealing time is too long, continuous annealing may become difficult.
  • the annealing time of the grain growth may be 65 seconds to 330 seconds from the viewpoint of increasing the economic feasibility.
  • the grain growth may be performed in a nitrogen and hydrogen atmosphere, and it may include 51 vol% or more of hydrogen.
  • the slab was reheated at 1150° C. and then hot-rolled to 2.0 mm to manufacture a hot-rolled steel sheet.
  • the hot-rolled steel sheet was annealed at 1100° C. for 100 seconds, and then slowly cooled at 750° C. and then air-cooled. After that, the steel sheet was pickled and then cold-rolled to 0.27 mm.
  • grain growth annealing was performed after nitriding-annealing, and the temperature of the nitriding-annealing and the nitriding amount were as follows. The temperature of the grain growth was also changed as shown in Table 1. For the time of the grain growth, the final annealing was performed for 300 seconds to manufacture an electrical steel sheet. In this case, the temperature increase rate up to the nitriding treatment temperature was as shown in Table 1.
  • Magnetism was measured for the electrical steel sheet manufactured as described above, and in this case, the magnetism of the steel sheet was measured in the rolling direction and the direction perpendicular to the rolling direction by using a 60X60 mm 2 size single sheet measuring device, and the measured results are expressed as an average value.
  • the azimuth fraction was calculated through EBSD measurement, and the results are shown in Table 2 below.
  • the surface layer portion is up to a thickness of 15 % from each of both surfaces, and the central portion is an inner portion of the surface layer portion.
  • Comparative Material 1 to Comparative Material 3 did not undergo the nitriding-annealing, so that the grain sizes of the surface layer portion and the central portion were not properly adjusted, and the magnetism was inferior.
  • Comparative Material 4 had a small grain size at the center portion and the magnetism was inferior because the temperature increase rate was too low.
  • Comparative Material 5 had a small amount of nitriding, so that it had a large grain size in the surface layer portion, poor high-frequency iron loss, and poor strength.
  • Comparative Material 6 had a small grain size at the center portion and the magnetism was inferior because the amount of nitriding was too high.
  • Comparative Material 7 had an excessively high grain growth annealing temperature, so that the grain size in the center portion was too large, and the magnetism and strength were inferior.
  • FIG. 1 shows the result of observing the cross-section of the steel sheet of Inventive Material 1. As shown in FIG. 1 , it can be confirmed that the grain sizes of the surface layer portion and the central portion were different from each other.
  • the slab was reheated at 1150° C. and then hot-rolled to 1.6 mm to manufacture a hot-rolled steel sheet.
  • the hot-rolled steel sheet was annealed at 1100° C. for 100 seconds, and then slowly cooled at 750° C. and then air-cooled. After that, the steel sheet was pickled and then cold-rolled to 0.27 mm.
  • the following three comparative examples were not nitrided, and the remaining comparative examples were nitrided at 780° C.
  • a PH 2 O/PH 2 value of the oxidation degree is 0.00076
  • the temperature increase rate from 300° C. to 780° C. was as shown in Table 3.
  • the close contacting property was evaluated by a 15 mm ⁇ bending test. When peeling did not occur, it was indicated as good, and when peeling occurred, it was indicated as bad.
  • Comparative Examples 8, 9, and 10 did not properly include Si and Sn and did not undergo the nitriding-annealing, so that the texture was not improved and the magnetism was inferior.
  • Comparative Example 11 did not properly include Sn, so that the texture was not improved and the magnetism was inferior. In addition, it can be confirmed that the close contacting property was inferior.
  • the slab was reheated at 1150° C. and then hot-rolled to 2.0 mm to manufacture a hot-rolled steel sheet.
  • the cold-rolled steel sheet and the non-cold-rolled steel sheet were annealed for this steel sheet to the thickness shown in Table 5 below. It was performed at 1100° C. as an annealing condition, and then slowly cooled to 750° C., and then air-cooled. Thereafter, the steel sheet was pickled, and cold-rolled to 0.27 mm, and then the cold-rolled steel sheet was final annealed.
  • the temperature increase rate was increased to 40° C./s
  • the nitriding-annealing was performed at 780° C. with a nitriding amount of 35 ppm
  • the grain growth annealing was performed at the temperature of Table 5 for 300 seconds.

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